Electron tube



Jan. 17, 1956 J. A. M CULLOUGH 2,731,573

ELECTRON TUBE Filed April 50, 1951 Sheets-Sheet 1 dual? ,4. ME Cu//ou BY621 A TTOPNEY Jan. 17, 1956' Filed April 30, 1951 J. A. M CULLOUGHELECTRON TUBE 3 Sheets-Sheet 2 To E/Ybausf Pam a INVENTOR. JackAMfiCu/lough ATTORNEY Jan. 17, 1956 .1. A. MOCULLOUGH ELECTRON TUBE 5Sheets-Sheet 3 Filed April 30, 1951 7b Ex/iaus? Pam 9 INVENTOR. Jack A.Ms Cu/lougfi BY Mg 7 ATTORNEY the general shape of a flat cylinder.

United States Patent C) ELECTRON TUBE Jack A. McCullough, Millbrae,Calif., assignor to Eitel- McCullough, Inc., San Bruno, Califi, acorporaticn of California Application April 30, 1951, Serial No. 223,708

8 Claims. (Cl. 313-245) My invention relates to an electron tubeembodying a ceramic construction such as disclosed in the copendingapplication of Harold E. Sorg et al., Serial No. 202,666, now Patent No.2,647,218, and more particularly to improvements adapted for small tubestructures such as those in the receiving tube category.

Receiving tubes as made in the past have served a good purpose but theyhave left much to be desired in matters of dependability and ruggedness,the shortcomings being largely due to the mechanical construction of theglass tubes which had grown out of the old lamp industry.

It is among the objects of my invention to overcome the abovelimitations and to provide a tube of compact and rugged construction.

Another object is to provide a tube which is easy to fabricate andassemble.

A further object is to provide a tube of the character described havingtwo electrode assemblies in the same envelope.

A still further object is to provide an improved method of assemblingand evacuating the envelope.

'The invention possesses other objects and features of advantage, someof which, with the foregoing, will be set 'forth in the followingdescription of my invention. It is to be understood that I do not limitmyself to this disclosure of species of my invention as I may adoptvariant embodiments thereof within the scope of the claims.

Referring to the drawings:

Figure 1 is a plan view of a tube embodying the improvements of myinvention; and

Figure 2 is a sectional view of the same taken in a plane indicated byline 2-2 of Figure 1.

Figures 3 and 4 are sectional views showing the tube in a bell jarduring the exhaust operation.

In terms of broad inclusion, a twin triode type of tube embodying myinvention comprises an envelope having The envelope is made up ofceramic sections including two disk-like end wall pieces and two alignedcylindrical side wall pieces. These ceramic sections have metalizedabutting edges which are brazed together to form a vacuum-tightenvelope. A cathode, common to both triode units, composes a flat buttonhaving a suitable heater and is supported on a transverse metal diskcentrally of the envelope, the edge of which disk is connected to thebraze between the side wall cylinders. Two disk-like grids on oppositesides of the cathode are supported on metal terminal pins extendingthrough the end walls. The ceramic end wall sections also function asanodes and have their inner faces metalized for that purpose, thesemetalized areas being connected to the end wall brazes. Terminals forthe anodes and cathode are provided by metalized areas on the ceramicenvelope adjacent the respective brazed joints.

In greater detail and referring to Figures 1 and 2, my improved tube isshown as a twin triode suitable for tube uses normally classed asreceiving tubes. Tubes in this category in the past have been of glassor glass and metal ice construction with electrode assemblies supportedwithin the envelope by transverse insulators such as mica sheets and thelike. In my tube no glass or complicated glass and metal construction isemployed, and the internal insulators are eliminated.

The improved tube has the general shape of a flat cylinder and does notinvolve the usual type of socket arrangements. For a tube having a platedissipation of about 15 watts per anode, the tube would be aboutonethird the size of that shown in Figures 1 and 2. The envelope is madeup of four ceramic sections including two disk-shaped end wall sections2 and two aligned cylindrical side wall sections 3. The end pieces 2 areof identical shape and the side wall pieces 3 are also shaped alike sothat actually there are only two different kinds of ceramic pieces usedin making up the envelope.

The envelope sections are fitted together along abutting edges, endsections 2 being preferably recessed at the periphery to receive theside wall cylinders and the central abutting edges of the side wallsections 3 being preferably recessed to provide'a circular groove forpurposes hereinafter described. These ceramic sections are metallicallybonded together at the joints to form vacuum-tight seals; the sidesections being united by a metallic bond 4 and the end sections beingunited to the side cylinders by the bonds 6. These bonding layers extendalong the abutting surfaces between the parts from the inside to theoutside of the envelope and also function as lead-in conductors to theelectrodes.

The ceramic used in making up the envelope may be of any suitableceramic-like material, such as the alumina or zircon type ceramic bodiescommercially available. Metallic bonds 4 and 6 forming the vacuum-tightseals may be made in several ways, utilizing known metalizing andbrazing techniques. For example, the opposed surfaces of the ceramicpieces may be coated with finely divided molybdenum powder, or a mixtureof molybdenum and iron powders or the like, and then fired in hydrogento a temperature of about 1500" C. to sinter the metal powder to theceramic surface. This produces a thin metallic layer firmly bonded tothe ceramic. Such metallized surfaces may then be brazed or solderedtogether with silver solder or brazing alloys such as silver-copper, orgoldcopper or the like. The brazes are readily made by fitting themetallized ceramic pieces together with rings of Wire solder adjacentthe joints, and then elevating the temperature of the whole up to themelting point of the solder in a suitable furnace.

In the planar electrode tube illustrated having an indirectly heatedcathode, the latter comprises a flat buttonlike cathode 7 of a metalsuch as nickel having parallel surfaces coated with an electron emissivematerial such as the conventional barium-strontium oxides. This cathodeis supported by metal ring 8 in which the cathode button is inserted,the ring being engaged along its periphery by the circular groove formedby the recesses previously mentioned in the ceramic side wall sections3. The interfitted relationship of these parts also provides means forcoaxially aligning the side Wall sections when these wall sections areassembled. When the parts are bonded together at the braze 4 the latterprovides the cathode lead-in conductor through the side wall of theenvelope.

Cathode terminal 9. on the envelope is preferably formed by a metalizedarea on the ceramic sections connected to the lead-in braze 4. Thus,when the edges of ceramic sections 3 are treated, as bymolybdenumsintering, to metalize the region adjacent the joint, themetalized areas are preferably extended over the outer surfaces toprovide a metal band around the body of the envelope to form theterminal 9.

The heater for cathode 7 preferably comprises a flat spiral of heaterwire 11 embedded in a suitable insulating material 12 within the cathodebutton. One end of the heater coil is connected to the cathode and theother end brought out through a metal lead 14 brazed in a .side Wallsection 3.

Control grids 15 of :the .twin-triodeiillustratedrarepreferablydisk-shaped [grids having parallel wires fastened to retaining rings 17,these grids .being disposed unopposite sides of cathode and paralleltherewith. Grid rings 17 are supported on metal leads .28 extendingthrough and brazedrto thezceramic. end walls .2.

ably threeof these supporting-leads for each of the grids. The holesthrough which the leadsrextencl .are preferably rmetalized land :theleads secured by =ceramic-to-metal brazes.

In my improved tube. the end wall sections ;2 of the envelope alsoserveas the :anodes, Ltheionerfaces .Cdthe ceramic sections being'rnetalized, as by .molybdenum 'sint'eringto provide .theactive anodesurfacesfi. Ceramics such 'as'thealumin'a type ceramicbodies are. quitegood heat "conductors and will zadequately dissipate the heat in smalltubes having relatively low anode dissipation ratings. The areasaround-thegrid .leadsarenot .metalized so as to iusulate the anodefrornth'e grids. A-convenieut way to do thisis'to provide recesses Zlaroundleads 19 and metalizc 'only the flat faces of the ceramic anodes.

.Brazcs function'asthe anode lead-in conductors and anode terminals 22are preferably formed by metalized areas on the ceramic envelope. Thuswhen the ceramic pieces are treated, asby molybdenum sintering,tometalize the regionsadjacent the joint, the metalized areasarepreferably extended over the outer surfaces to provide metal bandsaround the body of the envelope to form the terminals 22.

The brazes at'the joints and metalized areas are shown as havingappreciable thickness for convenience of illustration. Actually, theseare quite thin metal layers, say

of the order of 0.062" totLOOS" thickness, and appear as films or metalskins on the surfaces of the ceramic. If desired, silver, copper or thelike may be-electrop'lated or flowed over thesintered'areas to furtherimprove the electrical conductivity. Copper "01' silver plating on thesintered areas, forexample, make-excellent terminal surfaces and isideal for brazing together at the joints'either wither without the useof additi-ve brazing material.

In my tube a suitable 'pumpingtubulation (not shown) may be provided'for evacuating the envelope. Such a .tubu'lation maybe of metal brazedtoa wall of the envelope and pinched off in the usual manner afterexhaust. With this conventional purnping procedure the ceramic envelopesections would be completely brazed together mall the joints in asuitable furnace before connecting the t ibe ;to a .vaeunm pump.

An improved method of pumping the tube-embodying my invention, :whichdoes not require a tribulation on the envelope, isilIustrated'in-Figures 3 and 4. case the tube, partially disassembled,is placed in a bell jar 23 seated on a base plate '24 having a duct'zleading to. an exhaust pump. At the stage shown in Figure 3 the tubepreferably comprises three subassemblies, namely,

the central assembly comprising cathode 7 mounted on the previouslybrazed Wall sections 3, and the end assemblies comprisinggrids 16mounted on anode sections 2. These three units, with the end assembliesseparated'frorn the central assemblyyare held by any suitable fixture(not shown) so that the space .between'the tube parts-is evacuated whenthe bell jar is exhausted. Such fixture .is so arranged that the endassemblies are permitted to collapse together against the centralassembly to close thesenvelopeafter exhaust of the bell jar.

When using this exhaust procedure the final brazes betweencerami'csectionsiand 3 are made in the bell jar. The brazing material, such assilver or copper, is previously applied to the ceramic parts byelectroplating or flowing the metal over the sintered'areas ashereiobefore mentioned. The brazing'operation then merely-in- Therearepre'ferin this bell jar is first exhausted to a hard vacuum. All thetube assemblies are then preferably heated sufiiciently to outgas thetube parts. This-corresponds tothe usual bake out step; the addedadvantage in my process being that the tube is open "at this time 'sothat the gases-are quickly pumped away, resulting 'in a more "completeoutga'ssing of the parts. A simple way of heating the parts forbake outpurposes isto .use ametalcylindetuZTiu.the bell jar heated by inductionfrom an external radio-frequency coil 28.

After. outgassing the tube parts the oxide cathode 7 is activated. Thisis also done while the envelope is in th open position showniinfigure 3.Activation of thc cathodew coating accomplished y heatingtm cathod.withheater ll'zto fllQPI'opGl. forming temperaturein ihfi usual,manner. the heater current in supp e im-my case hrough suitable leadsentering the hell iar anticoanected to the heater terminals. llfheadladadvantagein .mvprocws is that cathode activation takesplace wi h dnger oictmtamimfing the grids and other italpart of the tube. Thisovercomes a serious 'problem in the making f oxide eoatedtypesofitubes,because ordinarily tube parts such as grids which are closely spaced tothe cathodelare vulnerable to contamination by barium and other activeagents volatilized from the coating during cathode formation. With myprocedure there is much less likelihood of such contamination because,the gridanode assemblies are further separated from thecalhode; .andthe. envelope being open allows the volatile :con- .stituentstobeguicklypumped away.

After the cathode has been formed, the end assembliesare moved intoposition, against theside :wall-sections to close the envelope :asishownin Figure-4, and the final brazes are made by bringing thetemperature ofv'the metalized ceramicand joints up to the melting.poiutof the metal-to-metal surfaces. Such heating is preferablylocalized .at.the.-j,oints, :as byradiation.fromadjaeent heater coils.29.. Upon completion :of the brazes the exhaus pumpis ,shuttofifandathecompletcd tube is ready for removal from the bell jar.

I claim:

1. An electron tubecomprising an envelope having a cylindricalceramic-side wall and-a disk-alike ceramic @Clld wall, the inner .faceof the end wall being metalized pr iding an anode, a cathode :carried bythe side wall and having aneleflroo :emittingsuriaceiymg parallel withtire-anode,a disk-like .grid interposed between the catho eandauodasupportiugleads to the grid extendi s throug end wall, and .ametallic bond uniting th amic wside ar d-end walls and forming a lead iuconnection to the anode.

'2. electron tube comprising an envelope having a cylindrical ceramicside wall. and disk-like ceramic .end walls, said side wall comprising apair ofaligned sections, the inner :facesofthe end walls ,belngmetalizedproviding anodes, a cathode supported from the "side wall and havingelectron emitting surfaces lying parallel with saidanodesa metallic bonduniting the ceramic side wallxsections and forming a lead-in connectionto the cathode, disk-like .gt'idsinterposed between the oathode andanodes, supporting leads to the grids extending through-the end walls,.andmetal-lic bonds uniting the ceramic side and end wallsand forming'leaddn connec- .tions to the anodes.

3. Aurelectron tube comprising 'a generally cylindrical envelope havingupper and lower disk-like walls Oi ceramic, a cylindrical sidewall ofceramic "titted to theend walls alongupper an'dlowerjoints, metallicbonds metallic bonds at the upper and lower joints providing lead-inconductors for the anodes, and a cathode in the envelope supported onthe side wall and having electron emitting surfaces facing the anodes.

4. An electron tube comprising a generally cylindrical envelope havingupper and lower disk-like end walls of ceramic, a cylindrical side wallof ceramic fitted to the end walls along upper and lower joints,metallic bonds uniting the ceramic parts at said joints, the inner facesof the end walls being metalized providing anodes, said metallic bondsat the upper and lower joints providing lead-in conductors for theanodes, a cathode in the envelope supported on the side wall and havingelectron emitting surfaces facing the anodes, and disk-like grids in theenvelope interposed between said cathode and anodes.

5. An electron tube comprising a generally cylindrical envelope havingupper and lower disk-like end walls of ceramic, a cylindrical side wallof ceramic fitted to the end walls along upper and lower joints,metallic bonds uniting the ceramic parts at said joints, the inner facesof the end Walls being metalized providing anodes, said metallic bondsat the upper and lower joints providing lead-in conductors for theanodes, said side wall comprising sections fitted together at a jointlying intermediate the end walls, a metallic bond uniting the side wallsections at said intermediate joint, and a cathode in the envelopesupported on the side wall and having electron emitting surfaces facingthe anodes, said metallie bond at the intermediate joint providing alead-in conductor for the cathode.

6. An electron tube comprising a generally cylindrical envelope havingupper and lower disk-like end walls of ceramic, a cylindrical side wallof ceramic fitted in the end walls along upper and lower joints,metallic bonds uniting the ceramic parts at said joints, the inner facesof the end walls being metalized providing anodes, said metallic bondsat the upper and lower joints providing lead-in conductors for theanodes, said side wall comprising sections fitted together at a jointlying intermediate the end walls, a metallic bond uniting the side wallsections at said intermediate joint, a cathode in the envelope supportedon the side wall and having electron emitting surfaces facing theanodes, said metallic bond at the intermediate joint providing a lead-inconductor for the cathode, disk-like grids in the envelope interposedbetween said cathode and anodes, and supporting leads for the gridsextending through the end walls.

7. A stacked ceramic type electron tube comprising an envelope havingthe shape of a flat cylinder with side and end walls, the side wallcomprising metalized ceramic rings sealed in a vertical stack andproviding an annular side wall joint between a pair of said rings, ametallic layer uniting the metalized ceramic rings at said joint, one ofsaid end walls providing an anode having an inner anode surface lyingsubstantially parallel with the plane of said joint, a cathode structurein the envelope having an emitting surface substantially parallel withsaid anode surface, a conductive support for said cathode extendinginwardly from said side wall joint, and a terminal on the envelopeconnected to said cathode support through the metallic layer of saidjoint.

8. A stacked ceramic type electron tube comprising an envelope havingthe shape of a flat cylinder with side and end walls, the side wallcomprising metalized ceramic rings sealed in a vertical stack andproviding an annular side wall joint between a pair of said rings, ametallic layer uniting the metalized ceramic rings at said joint, saidend walls providing anodes having inner anode surfaces lyingsubstantially parallel with the plane of said joint, a central cathodestiucture in the envelope having upper and lower emitting surfacessubstantially parallel with said anode surfaces, a heater for thecathode interposed between said emitting surfaces, a conductive supportfor said cathode extending inwardly from said side wall joint, and aterminal on the envelope connected to said cathode through the metalliclayer of said joint.

References Cited in the file of this patent UNITED STATES PATENTS2,099,531 Passarge Nov. 16, 1937 2,167,515 Katsch July 25, 19392,200,911 Bowie May 14, 1940 2,351,895 Allerding June 20, 1944 2,371,683Eitel et al. Mar. 20, 1945 2,422,945 Brian June 24, 1947 2,425,593 BrianAug. 12, 1947 2,428,610 Beggs Oct. 7, 1947 2,647,218 Sorg June 28, 1953

